1. Field of Invention
The present invention relates to methods, systems, apparatus and products relating to drawing and blowing of ultra thin glass substrates, such as flexible display glass sheets for use in organic light emitting diode (OLED) displays.
2. Description of Related Art
Producing flat product glass for displays, such as OLEDS and liquid crystal displays (LCDs), involves many challenges. While LCDs typically require rigid display glass having minimal product distortion, such as arises due to internal stresses in large product glass plates, OLED technology is moving in the direction of providing flexible displays. Therefore, flexible polymer substrates are under investigation for use in OLED displays. Glass, however, is not generally a very flexible material, except possibly when the glass is ultra thin, so using glass in the creation of flexible OLED displays would require creation of glass thin enough to flex without breaking.
Organic light emitting diodes have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). Some OLED displays are known as being very bright and having a good color contrast and wide viewing angle. However, the traditional OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. The life of the OLED display can be increased significantly if the electrodes and organic layers within the OLED display are hermetically sealed from the ambient environment.
Another challenge, therefore, with the creation of an OLED display is the requirement that the OLED display seal out moisture and oxygen, which may destroy the OLEDs if they permeate the display. For instance, the hermetic seal should provide a barrier for oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day). A disadvantage of polymer substrates, though, is their susceptibility to permeation of moisture and oxygen. Glass, however, is one of the few materials simultaneously offering transparency, a scalable surface, and an efficient, long term barrier to oxygen and moisture. These properties are required for current, and most of future, display panels, on at least one side of the device. As such, glass remains a prime candidate for OLED display manufacture. For instance, rigid OLED displays may use rigid sheets of glass to encase the OLED pixels, which then may be hermetically sealed using a frit seal.
The flexibility of glass can be characterized by the radius of curvature, typically ranging from 10 mm to 10 cm, for example. In contrast to flat, thin, but rigid current LCD displays, the flexible OLED displays need a flexible substrate, possibly both in a roll-to-roll manufacturing process as well as in the device itself. The glass thickness compatible with such radius at an admissible stress level is respectively in the order of 10 to 30 μm.
Producing such thin glass sheet is still a tenuous task using techniques of the prior art. Known fusion draw or down draw processes are usually limited to producing glass of thickness of 100 μm, but they are limited also in width because of side reduction while drawing. It would therefore be desirable to develop a new process for ultra thin glass manufacturing for production of flexible glass substrates.